1. Field of the Invention
The invention relates to the equipment for arc welding, in particular, and it deals with an apparatus for overhead submerged arc welding.
2. Description of the Related Art
A large volume of operations in the manufacture of welded structures is carried out in welding rotatable annular joints of hollow structures with a restricted access to joints being welded on the inner side of the structure. Such joints include annular joints of closed vessels, annular joints of pipelines, tanks, casings, field welds and shell plating seams of ship hulls; longitudinal joints of large-area products which cannot be positioned to facilitate welding. They also include joints of difficult-to-position webs, segments, three-dimensional and planar sections, and the like.
A submerged arc overhead welding method is characterized in that a consumble electrode and a welding bath are turned at 180.degree. in comparison with downhand welding. Flux an electrode are fed to the work from bottom up, i.e. as though towards a ceiling, the electrode being supplied through a compacted flux.
This welding method is referred to hereinbelow as overhead submerged arc welding.
This welding method is referred to as the overhead submerged arc welding also because the arc is in the body of metal.
So called overhead welds are produced as a result of such welding.
Overhead welds may be of different types, e.g. penetration overhead welds, sealing overhead welds. There may be one-pass overhead welds and other types of overhead welds.
The penetration overhead welds are welds which are first to be produced in welding a joint and which are located in the top part of sections being welded on the joint side opposite with respect to the electrode supply. Further welding of the joint, i.e. producing the necessary subsequent welds is carried out by any appropriate known method, the electrode being supplied on the same side as is the case with welding of the overhead penetration weld, e.g. the inner penetration welds of rotatable annular joints of vessels, tanks, joints between bottom sections of shell plating of ships and other structures.
The overhead penetration weld arc welding allows, to a large extent, the operation of welding from the interior of a vessel to be dispensed with in welding rotatable annular welds, and welding in confined spaces in producing straight welds of structures with a restricted access on the side of a ceiling can also be eliminated.
The sealing overhead welds are welds which are first to be produced in welding a joint and which are located in the bottom part of sections being welded on the electrode supply side of the joint. Further welding is carried out by any appropriate known method with the electrode supply on the side of the joint being welded opposite to that used in the overhead welding.
In practice, the penetration overhead welds are produced in welding annular and longitudinal joints of structures with a restricted access to joints being welded from the inside, the sealing welds being produced in welding longitudinal joints of difficult-to-position products, e.g. plate structures made out of segments, and other products.
One-pass overhead welds include welds produced in welding joints of a limited thickness arranged over the whole welded section. No further welding of the joint on any side thereof will be required.
Welding of sealing and one-pass welds poses many problems concerned with the formation of the surface of a finished weld.
During the overhead welding, the welding bath metal formed during arcing by fusion of the metal being welded, electrode material and flux is retained by a crust of partly melted flux and also by means of forming members. The forming members may be of various shapes and size and may be made, e.g. in the form of plates, backings, bars, sliders and other members and structures.
Flux is pressed against the welding zone positively from bottom up and, as flux is being consumed, its stock is continually replenished. For forming the top part of a weld, flux may be supplied both on the bottom side, through the gap between the edges of a product being welded, and from top by any appropriate known method by which a filled layer of flux is formed. Special forming backings or flux holding means may also be used.
Numerous problems arise especially in welding hard to get at joints of large-size products of cylindrical or like configuration such as ship hulls and boiler units where especially high quality of welds is required and where the products must be rotated about their axis during welding operations, as well as in welding large-area planar products which it is very difficult to place in a position facilitating the welding.
Known in the art is an apparatus for overhead submerged arc welding (SU, A, 469554), comprising a hopper containing flux and a bowl for supplying flux thereto and for pressing flux against the work. The bowl has an outlet port facing towards the joint being welded and an inlet port for supplying flux to the bowl and for creating a desired pressure of flux in the bowl. Flux is supplied by a pipe communicating with the inlet port of the bowl. The pipe has a flux supply means in the form of an auger.
A welding nozzle through which the consumable electrode is supplied is provided in the bowl adjacent to the inlet port and a pivotally mounted adjusting plate located downstream of the welding nozzle is provided on the side of the bowl opposite to the inlet port.
For varying the angle of inclination with respect to the outlet port of the bowl, the adjusting plate has an adjusting screw.
This apparatus provided with the adjusting plate allows preset flux pressure to be controlled during welding at different points along the joint being welded.
During welding by means of this apparatus, the operator keep an eye on the joint being welded and, if parameters of the joint, e.g. the amount of clearance between the edges of the structure deviate from preset values, the operator can correct the situation by acting upon the screw to vary the angle of inclination of the plate so as to maintain the desired flux pressure since it is very important that preset flux pressure values for high-quality overhead welding be maintained with maximum possible accuracy at various points along the joint being welded because otherwise the weld would be of poor quality.
The abovedescribed apparatus cannot, however, ensure an automatic maintenance of preset flux pressure values at various points along the joint being welded without operator's interference. During welding with this apparatus, it is necessary to continually vary position of the adjusting plate so that the operator must be continually involved and must pay a special attention during welding, the operator having to be very skillful. Consequently, quality of weld in welding with the aid of this apparatus depends on the operator's skill and experience which may not unfrequently result in low-quality welds.
In addition, the experience of operation of such an apparatus showed that it is suitable for welding joints having minimum deviations of parameters of their assembly before welding (e.g. misalignment of the plate edges, gap, V-section, etc.) and cannot be used for welding elongated products or annular joints, especially of large-diameter structures.
Known in the art is an apparatus for overhead arc welding (FR, B, 2568808), comprising a hopper containing flux and accommodating a bowl having an inlet port and an outlet port, the inlet port communicating with a flux supply pipe. A welding nozzle for supplying a consumable electrode is provided in the bowl. The bowl cooperates with a forming means having an adjusting bar for providing different pressures of flux at various points along the joint being welded, a part of the forming means being located directly in the bowl, adjacent to the consumable electrode.
The hopper supports a means for supplying the electrode to the welding nozzle, and the hopper is mounted on a suspension by means of a pivot pin for rotation about this pivot pin and has a point-like contact copying member which is located substantially in line with the adjusting bar. The adjusting bar also has a pair of copying members and is mounted for longitudinal and transverse swinging movements.
In addition, the hopper is provided with a means for pressing the hopper proper and the copying member against the work being welded.
This apparatus for overhead welding can substantially automatically maintain the stability of flux pressures necessary for carrying out high-quality welding at various points along the joint being welded. Participation of the operator in controlling welding process is substantially dispensed with, especially in welding elongated products of a regular geometry (and more especially, of cylindrical and straight products), deviations from joint assembly parameters before welding being compensated for.
This apparatus makes it possible to implement the method of overhead submerged arc welding in which different present flux pressure values are automatically maintained at various points along the joint being welded during welding so as to produce high-quality penetration overhead welds.
This construction of the apparatus ensures a reliable retention of a welding bath during welding at the level of the joint being welded and the formation of high-quality welds with the desired formation of reinforcement on the inner side of the weld (on the side opposite to the ceiling), i.e. in producing penetration overhead welds.
However, the welds produced in this manner have deviations of shape of the outer side of the finished weld admissible for the penetration weld, in the form of irregularities, undercuts, local weld width fluctuations and other defects on the outer side of the weld which will require further rewelding to provide a next layer.
These defects in forming the outer side of the weld can be explained by inadequate conditions provided by this apparatus for jamming and retaining flux at various points before the formation of welding bath and in the welding zone. In addition, this apparatus does not allow high-grade copying of the surface of the welded joint to be carried out directly adjacent to the point of welding which is necessary to producing sealing overhead welds, and especially one-pass overhead welds.
Moreover, this apparatus cannot provide maximum favorable conditions for copying position of the working surface of the bar with respect to the surface of the joint being welded in cases of a substantial deviation of its surface from regular geometry. This is due to the relative position of the copying members and their position with respect to the welding bath which is not quite optimum as it is necessary for producing sealing and one-pass overhead welds. Investigations have shown that the copying members should be located as close as possible to the welding bath (welding zone).